Gas driven turbines have been employed previously for holding the samples to be investigated in the high intensity unidirectional magnetic field of a nuclear magnetic resonance spectrometer while at the same time rapidly spinning the sample tube about its axis. Spinning of the sample averages out the effects of inhomogeneity in the polarizing magnetic field, enabling improvement in the resolution of the resonance lines of the spectrum. The spinning sample technique is disclosed in U.S. Pat. No. 2,960,649 issued Nov. 15, 1960.
Heretofore turbines for the smaller diameter sample spinners took the form of elongated cylindrical members having an axial bore therethrough which bore was provided with slotted extensions at its top or bottom end. At some location in the bore, its diameter was made to be slightly smaller than the outside diameter of a sample tube to be inserted, therein enabling an inwardly acting force upon the sample tube upon insertion. The alignment of the sample tube to the axis of the turbine was thereby determined by the bore and concentricity of the bore. Since the axial bore has to be large enough to receive the expected tolerance in sample tube sizes, normally the tubes would be grasped by the turbine at only one location, resulting in a wobble of the sample tube upon spinning. With very small amounts of sample and hence low level signal, this instrumentation artifact was particularly undesirable. In order to assure concentricity of the inner bore, expensive machining of the turbines was required since it is difficult to maintain concentricity of a small bore over a long length.